The long term goal of this proposal is to identify the signal transduction pathway(s) by which free fatty acids (FFA) exert their effect on calcium homeostasis and the consequent biological response of endothelial cells. In vivo studies in humans have demonstrated that elevation of plasma fatty acids causes dysfunction of endothelium dependent vessel relaxation. Exposure of cultured endothelial cells to FFA also diminishes G protein coupled receptor (GPCR) induced Ca2+ signaling and NO production. The key question to be explored in the current proposal is how FFA inhibit GPCR induced Ca2+ signaling in human endothelial cells. The specific objectives of the current proposal are: Specific Aim 1. Investigate the effects of FFA on GPCR and thapsigargin (Tg) induced Ca2+ signaling in human abdominal aortic endothelial (HAAE) cells; Specific Aim 2. Investigate the effect of FFA on mitochondrial functions in HAAE cells; Specific Aim 3. Determine the role of mitochondria in the inhibition of GPCR induced Ca2+ signaling by FFA; Specific Aim 4. Determine the specific mitochondrial pathway(s) involved in FFA inhibition of GPCR induced Ca2+ signaling in HAAE cells. This proposal will use modern fluorescent imaging techniques, mitochondrial targeted gene expression and other molecular biological methods to investigate the effects of FFA on GPCR mediated Ca2+ mobilization, mitochondrial electrochemical potential and other mitochondrial functions. Mitochondrial DNA depleted HAAE cell model will be created and used to evaluate the role of mitochondria in FFA inhibition of GPCR induced Ca2+ signaling. Furthermore, in this proposal I will also explore the role of the FFA activated, uncoupling protein 2 mediated mitochondrial proton transport, in FFA inhibition of GPCR induced Ca2+ signaling using gene targeted approach. Overall, this proposal will provide mechanistic data that will help our understanding of the pathogenic role of FFA in diabetes and its cardiovascular complications.